1. Field of the Invention
The present invention relates to a lock with improved torsional strength, and more particularly to a cylindrical tubular lock having an outer handle.
2. Description of the Related Art
U.S. Pat. No. 4,966,399 issued to Lin on Oct. 30, 1990 discloses a cylindrical lock comprising an outside knob 2 that includes a replacing plate 26 attached to an end of the knob 2, a square shaft 25 extended through the replacing plate 26, and an outside grip 21 engaged with a shaft hole 222 of an outside knob cap 22. Two placing notches 223 are symmetrically set at upper and lower edges of the shaft hole 22 for retaining two limit plates 28 in place. The limit plate 28 includes an L-shaped slot 281 through which a moving rod 29 extends. An end of the moving rod 29 is engaged with a lock core in the outside grip 21, and the other end of the moving rod 29 is engaged with a turning button 11 in the inside grip 12. The replacing plate 26 includes two curved slots 261 for engaging with the moving petal 212 of the outside grip 21.
It is, however, found that an unauthorized person may apply a relatively large torsional force to the outside grip to deform or bend the lockset and thus breaks the lockset. More specifically, the torsional strength of such a lock set is not enough. The present invention is intended to provide an improved design to solve this problem.